An active matrix display device has been known in which a plurality of pixels are arranged in matrix and each of the pixels includes a display element and a transistor as a switching element connected to the display element.
Further, an active matrix display device where a transistor formed using a metal oxide for a channel formation region is used as a switching element connected to each pixel electrode has attracted attention (see Patent Documents 1 and 2).
As examples of a display element applicable to an active matrix display device, a liquid crystal element and electronic ink using an electrophoretic method or the like can be given. An active matrix liquid crystal display device to which a liquid crystal element is applied has been used for a wide variety of applications ranging from display of a moving image taking advantage of high operating speed of the liquid crystal element to display of a still image with a wide range of gray levels.
[Reference]
    [Patent Document 1] Japanese Published Patent Application No. 2007-123861    [Patent Document 2] Japanese Published Patent Application No. 2007-096055